Generally, an intermediate transfer belt useful for a laser printer, a fax machine, and a copier should have excellent properties of heat dissipation, water repellency, oil repellency, contamination resistance, heat resistance, elastic modulus, releasability from paper, antistatic properties, and durability.
Further, upon long operation of the above apparatus, due to frictional heat caused between the intermediate transfer belt and the supplied paper in the printing process, considerable heat is generated at the interface therebetween, and thus heat dissipation properties for efficiently dissipating heat, which are regarded as important, are required. However, in the case where such heat dissipation properties are insufficient, the transfer belt becomes deformed due to frictional heat caused by long operation, thereby resulting in unreliable products. Moreover, high-temperature residual heat, which does not dissipate but remains in a small space, negatively affects peripheral devices, undesirably decreasing the lifetime of the peripheral devices and incurring the breakdown thereof.
In addition, the intermediate transfer belt should have volume resistivity suitable for realizing a toner transfer function. If the transfer belt has volume resistivity lower or higher than required, antistatic properties, transfer properties, imaging properties, releasability, contamination resistance and so on are deteriorated, and thus fatal defects, such as poor images, may occur.
Mainly used in a conventional intermediate transfer belt, a polyimide film has high heat stability and superior mechanical and electrical properties, but is very sensitive to moisture, undesirably reducing reliability with respect to electrical insulating properties over time. Also, since the polyimide film has a high glass transition temperature, processability thereof is limited and it easily becomes electrically charged. Further, the volume resistivity thereof is higher than the requirement for the intermediate transfer belt, hence it is difficult to use in the intermediate transfer belt.
In this regard, Japanese Unexamined Patent Publication Nos. 2003-270967, 2002-218339, and 2004-255828 disclose a method of producing a transfer belt, in which a polyamic acid solution, as a precursor of polyimide, is polymerized, placed in a mold, heat treated, further coated with a fluorine polymer compound for increasing releasability from paper, water repellency and oil repellency, and then heat treated.
However, the above method has many temporal, economical and physicochemical problems when actually used, attributable to the complicated process for additionally coating the partially cured polyamic acid solution with the fluorine polymer compound, the choice of a primer useful for adhesion between the polyimide layer, used as a substrate of the intermediate transfer belt, and the fluorine polymer layer, and stripping problems based on poor adhesion therebetween. Further, since a three-layer structure consisting of the polyimide layer, the primer layer, and the fluorine polymer compound layer is provided, the process becomes inefficient and complicated. That is, the thickness of the spray coated primer and fluorine polymer compound may not be uniform depending on working conditions and other factors, and as well, working efficiency is decreased because the process must be repeated several times.
Meanwhile, since the intermediate transfer belt of the laser printer, the fax machine and the copier plays a role in transferring the toner, it must be produced so as to be seamless. When a seamless intermediate transfer belt is produced in a conventional manner, a wash tub process, which realizes fast rotation using centrifugal molding, has been utilized. However, such a process suffers because it is difficult to use to produce a seamless intermediate transfer belt.